Solid state microwave heating apparatus

ABSTRACT

Apparatus for the treatment of materials by the application of heat for rapid drying, cooking or the like of the materials includes an enclosure having a plurality of solid state microwave generators generating signals at microwave frequencies. The generators are heat sinked to the inner wall of the enclosure and are coupled to at least one dipole antenna radiating into the enclosure for providing microwave heating in the enclosure.

1451 Sept. 12, 1972 United States Patent Chang [5 SOLID STATE MICROWAVE HEATING OTHER PUBLICATIONS APPARATUS RCA No. 812, Mailed Jan. 28, 1969; Solid State [72] Inventor: Microwave Oven by Erwin F. Belohovbek, 3 pp.

Kern KoNan Chang, Princeton, NJ.

[73] Assign: RCA Corponfion Primary Examiner-J. V. Truhe [22] Filed: Assistant Examiner-Hugh D. Jaeger Sept. 30, 1971 Attorney-Edward J. Norton ABSTRACT 21 Appl. No.: 185,067

m m l nm Med. al -m .W .m 8v Pm u t. 8 3%.... m m f om m i nWIc m Id m a u n was fed h. ufe mot a w Dam Acm 5 .l emu N93 Innmw 3m mu cl WW2 L mi CO .M mk UIF 1]] 218 555 [ll of solid state microwave generators generating signals References Cited UNITED STATES PATENTS at microwave frequencies. The generators are heat sinked to the inner wall of the enclosure and are coupled to at least one dipole antenna radiating into the enclosure for providing microwave heating in the enclosure.

I/l971 McAvoy.................219/1055 7 Claims, 5 Drawing Figures PATENTED SE? 12 I972 SHEET 1 OF 3 5 ii bDlODE 3| MODULES 38 {j 27 2 I L VARIABLE 37 D. c. BIAS 35 Fig. 1.

INVENTOR. Kern K.N. Chang A T TORNE Y PATENTEDSEP12I972 SHEEIEUFS INVENTOR. Kern K. N. Chang BY ATTORNEY PATENTEDSEPIZIHY? 3.691.338

' SHEET 3 [IF 3 INVENTOR. Kern K. N. Chang A T TORNE Y SOLID STATE MICROWAVE HEATING APPARATUS The invention herein described was made 'in the course of or under a contract or subcontract thereunder with the Department of the Air Force.

This invention relates, in general, to a microwave oven and more particularly to a microwave oven wherein a body located within the oven is heated by microwave power and by conventional heating.

Microwave heating is usually achieved by the use of a magnetron which has a relatively short lifespan. While it is known that solid statedevices which aregenerally more reliable can provide microwave signal generation, these devices are at best in the order of 50 to 60 percentefficient. Efficiency affects the cost of operating these devices.

Another problem associated with microwave ovens is the distribution of heat through the body placed in the oven to be heated. An uneven distribution of microwave energy within the oven causes uneven heat through the body located in the oven. Microwave energy may also tend to heat the body more on the inside than on the outside. This is contrary to conventional heating and as such is contrary to what people have become accustomed.

In accordance with this invention, an improved heating apparatus for utilizing microwave power is described. A plurality of solid state microwave generators are fixed to at least one inner wall of an enclosure. The inner wall to which the generators are fixed is configured and constructed for dissipating the heat associated with the operation of the generators into the enclosure and to thereby provide conventional heating of a body in the oven. At least one microwave antenna is coupled to the generators and is responsive to the generated signals from the generators for radiating said signals into the enclosure for causing microwave heating of the body therein.

A further description follows in conjunction with the following drawings wherein:

FIG. 1 is a diagrammatical perspective view partly broken away of an oven representing one embodiment of the invention.

FIG. 2 is a cross-sectional view of FIG. 1 taken along line 22.

FIG. 3 is a partial cross-sectional view of FIG. 2 taken along line 3-3.

FIG. 4 is a sketch of an alternative coupling arrangement to that shown in FIG. 1 in accordance with an embodiment of the invention.

FIG. 5 is a perspective view partly broken away of an oven representing another embodiment of the invention.

In FIG. 1 there is illustrated a cooking oven or enclosure having a cylindrical wall 11, a flat top wall 13 and a flat bottom wall 14. Access to the interior of the oven 10 may be provided by a hinged door structure 15 v in top wall 13. In the enclosure 10 there is provided four microwave radiating dipole antennas 17, 19, 21 and 23equally spaced from each other in the enclosure 10. The dipole antennas l7, 19, 21 and 23 each extend the same distance from the wall 11 of the enclosure 10. The cylindrical wall 11 is a multilayered structure. The inner surface layer 45 of the wall 11 is of metal to form a cylindrical reflector for each of the radiating elements 17, 19, 21 and 23. The next outer layer 49 is dielectric to which is fixed four narrow strip-like conductor networks 27A, 29A, 31A, and 33A.

A first cluster of eight solid state microwave signal generator modules 27 are attached to inner metal layer 45 of wall 11. The first cluster of module 27 have their output microwave signals coupled over narrow conductor network 27A to common region 28, which is coupled to the dipole antenna 17. A second cluster of eight solid state microwave signal generator modules 29 are fixed to inner metal layer 45 of wall 11. Likewise the microwave signals associated with the second cluster of modules 29 are combined at a common region 30 by the narrow conductor network 29A. These microwave signals from cluster of modules 29 are coupled to dipole antenna 19. A third cluster of eight solid state microwave signal generator modules 31 are fixed to metal layer 45 of wall 11. The microwave signals associated with the solid state modules 31 are coupled over narrow conductor network 31A to common region 32 and are coupled to dipole antenna 21. A fourth cluster of eight solidstate microwave signal generator modules 33 are fixed to metal layer 45 of wall 11. The output microwave signals from the solid state modules 33 are coupled over narrow conductor network 33A to common region 34 and are coupled to dipole antenna 23. Each of the eight modules in the first 27, second 29, third 31, and fourth cluster 33 of solid state modules are microwave signal oscillators preferably of either the transistor, Gunn or Avalanche type. The operation and construction of such oscillators is discussed in an article entitled Recent Advances in Solid State Microwave Generators pp. 44-86 of Advances in Microwaves, Vol. 2, 1967, Academic Press, Inc., New York. The required D.C electric field bias for the operation of these first 27, second 29, third 31,-and fourth 33 clusters of modules is provided by a variable D.C. bias source 35 over the respective leads 37, 38, 39 or 40.

A more detailed description of a cluster and an associated antenna element follows with reference to FIGS. 2 and 3. FIG. 2 is a partial cross-section of the cylindrical wall 11 taken in the general area of section 2-2 of FIG. 1 and particularly illustrating the inner surface of wall 11. FIG. 3 is a partial cross-section of cylindrical wall 11 taken in the general area of section 3-3 of FIG. 2. Referring to FIGS. 2 and 3, the inner surface of the wall 11 is a heat sinking conductive metal layer 45 which has a series of ridges 47 therealong which extend toward the inner surface of the enclosure 10 for dissipating heat. The next outer layer 49 from the metal layer 45 is made of dielectric material such as alumina. To this dielectric layer 49 is affixed the network of narrow conductors 31A coupling each of the solid state modules in the cluster 31 to each other at junction 32 and to the antenna feed 60.

Referring to FIGS. 2 and 3, the antenna feed 60 of dipole antenna 21 is made up of a coaxial transmission line having an outer conductor 59 and an inner conductor 61. The dipole antenna 21 comprises dipole halves 55 and 57 separated by dielectric member 56. The dipole antenna half 55 is coupled to the inner conductor 61 and the dipole antenna half 57 is coupled to the outer conductor 59. The outer conductor 59 of the transmission line extends to and terminates at the metal layer 45. The inner conductor 61 is coupled through an aperture 50 in the dielectric layer 49 to the junction region 32 of the network of narrow conductors 31A located on the outer surface of the wall 11. The solid state modules, for example, modules 65, 67 of the third cluster of solid state modules 31 are connected so that the microwave signals generated are coupled between the narrow conductor network 31A and the metal layer 45 as shown in FIG. 3 and so that each one of the solid state modules of the cluster of modules 31 is coupled in a heat sinking manner to inner metal layer 45 having the ridges 47.

A microstrip transmission line is formed by making the conductors of network 31A relatively narrow and spaced by the dielectric insulator or substrate layer 49 from the metal layer 45. Microwave signals generated at the eight modules of the cluster of modules 31 are coupled along the transmission line made up of narrow conductor network 31A and the metal layer 45 to the coaxial transmission line 60. These microwave signals are coupled along the coaxial transmission line 60 made up of inner conductor 61 and outer conductor 59 to the dipole antenna halves 55 and 57 of dipole antenna 21.

Due to the cylindrical shape and the fact that inner metal layer 45 of the wall 11 is of metal, the microwave signal energy radiated from each of the dipole antennas l7, 19, 21 and 23 sees a cylindrical reflector. This type of reflector provides with the dipole antennas oriented as shown in FIGS. 1 and 2 a relatively uniform electromagnetic field across the enclosure of the oven. Due to the ridges 47 in the metal layer 45, the conventional heat generated by the modules is better transmitted into the oven enclosure to heat the body therein. Since the wall 11 is substantially cylindrical, a body centered in the enclosure receives a rather uniform conventional heating. By controlling the DC. bias level to the modules at the bias source 35, the modules can be made to operate more or less efficiently in the generation of microwave signals and therefore provide either more or less microwave energy with more or less microwave heating in the enclosure. In this manner, control of the ratio of microwave heating to conventional heating can be provided. Such control is desirable to adjust for various types of foods, for example. Various tuning means could be placed along the transmission line formed by narrow conductor network 31A and layer 45 for improving both the impedance match and the operation of the solid state modules as is well known in the state of the art.

Referring to FIG 4, there is shown how isolation the modules from reflections at the antenna may be achieved if required by the use of a nonreciprocal device such as a microstrip circulator 64 which would permit the coupling of signals from the modules to the antenna but which would terminate the reflective signals from the antenna to a load rather than coupling back to the modules. Such a circulator as a described by Hershenov in US. Pat. No. 3,456,213 could be used with a first terminal 68 of circulator 64 coupled to a cluster of modules, the second terminal 66 in the direction of circulation (indicated by arrow 64A) coupled to an antenna and the third terminal 69 coupled to a load 68.

Referring to FIG. 5, an alternative approach to the arrangement discussed above is shown. In the alternative arrangement of FIG. 5, the oven enclosure is a spherically shaped structure 70. Six clusters of solid state modules 71, 73, 75, 77, 79 and 81 are equally distributed about the spherical structure 70. The innermost surface layer 92 of the oven would again be of heat sinking metal material followed by a dielectric layer 94. On the outer surface of dielectric layer 94 are six networks of narrow conductors 71A, 73A, 75A, 77A, 79A and 81A. The inner metal layer 92 together with the dielectric layer 94 and the narrow conductor networks 71A, 73A, 75A, and 81A form six networks of transmission lines for combining the microwave signals associated with each of the respective cluster of modules 71, 73,75, 77, 79 and81.

Six dipole antennas are coupled to the six cluster of modules such that the dipole antenna 82 is coupled to the cluster 71 of modules, dipole antenna 83 is coupled to cluster 73 of modules, dipole antenna 85 is coupled to cluster 75 of modules, dipole antenna 89 is coupled to cluster 79 of modules, dipole antenna 87 is coupled to luster 77 of modules and a dipole antenna (not shown) is coupled with the sixth cluster 81 of modules. In this case, the spherically shaped inner metal layer 92 would provide a parabolic reflector for each of the dipole antennas 82, 83, 85, 87 and 89. Again a DC. bias from source 96 would be coupled to each of the modules of the cluster of modules 71, 73, 75, 77, 79 and 81 over leads 91, 93, 95, 97, 98 and 99 respectively.

What is claimed is:

1. Heating apparatus utilizing microwave power comprising:

a plurality of solid state modules of the type which when biased generate microwave signals and heat,

a terminal coupled to said modules and adapted to be coupled to a bias source for providing biasing of said modules,

an enclosure having walls adapted to receive a body to be heated,

one of the inner surfaces of one of said walls being constructed of electrically conductive and heat conductive material and being configured to dissipate heat into said enclosure,

said plurality of solid state modules being fixed to said one inner surface of said one wall so that said heat generated from said modules is dissipated by said one inner surface of said one wall and in said enclosure for causing conventional heating of said body,

at least one microwave antenna being coupled to said modules and responsive to said generated microwave signals for radiating said microwave signals into said enclosure for causing microwave heating of said body.

2. The combination as claimed in claim 1, wherein means are provided for adjusting the operating characteristic of the modules for controlling the ratio of microwave heating to conventional heating in the enclosure.

3. The combination as claimed in claim 1, wherein said antenna is a dipole.

4. The combination as claimed in claim 3, wherein said inner surface of said one wall is cylindrically shaped to act as a cylindrical reflector for said dipole.

5. Heating apparatus utilizing microwave power comprising:

to receive a body to be heated, and a plurality of solid state modules of the type which when properly biased generate microwave signals and other about said cylindrical wall with said modules being fixed to said inner surface of said cylindrically shaped side wall so that said heat generated from said modules is dissipated in said enclosure heat, means for properly biasing said modules, the 5 for causing conventional heating of said body, innermost surface layer of said side wall being a at least four microwave antennas spaced from and metal conductor, the next outer layer adjacent said distributed equally about the inner surface of said innermost layer being of dielectric material having cylindrical side wall and extending into the interior on its outermost surface a network of narrow stripof said enclosure, means for coupling each of said like conductors joining said plurality of solid state 10 antennas to only one of said clusters of solid state modules to each other and forming with said modules so that microwave signals generated by dielectric layer and said innermost surface layer a said modules radiate from each of said antennas transmission line network for combining the into said enclosure for causing microwave heating microwave signals generated by each of said pluof said body. rality of solid state modules, said solid state 7. Heating apparatus utilizing microwave power modules being fixed to said innermost surface of comprising: said multilayered side wall so that heat generated a spherically shaped enclosure adapted to receive a from said modules'is dissipated in said enclosure body to be heated, the inner surface of said enclo- 'for causing conventional heating of said body, at sure being of electrically conductive and heat conleast one microwave antenna being coupled to said ductive material and being configured to dissipate modules over said transmission line network and heat into said enclosure, being responsive to said microwave signals for a plurality of solid state modules of the type which radiating said microwave signals generated at said when properly biased generate microwave signals modules into said enclosure and thereby causing and heat, said modules being fixed to said inner microwave heating of said body. surface of said spherically shaped walls so that said 6. Heating apparatus utilizing microwave power generated heat from said modules is dissipated comprising: uniformly in said enclosure for causing convenan enclosure adapted to receive a body to be heated having a cylindrically shaped side wall, a top wall and a bottom wall, at least four clusters of solid state modules of the tional heating of said body,

means for ro erl biasin sai modules, antenna m san eci ually sgare from each other and uniformly distributed from and about said inner type which when properly biased generate both microwave signals and heat,

means for properly biasing said modules,

surface of said spherically shaped enclosure, each of said antennas being coupled to a given number of modules and responsive to said microwave signals generated by said modules for radiating the inner surface of the cylindrically shaped side wall l f being metal with ridges therein to dissipate heat P energy sfqld enc Osure or into said enclosure, each of said clusters of solid Causmg mlcrowave heatmg ofsdld body' state modules being equally spaced from each UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,691,338 Dated September 12, 1972 Inventor(s) Kern KQNQ-D Chang It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 5, change "module" to -modules--.

Column 3, line 59, after "as" delete -a--.

Column 4, line 11, after "75A" insert -77A 79A Column 4, line 22, change "luster" to -cluster-,

Signed and sealed this 27th day of March 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PC1-1050 (10459) USCOMM-DC 60376-P69 l 2 U S. GOVERNMENY PRINYING OFFICE I969 O355-33 

1. Heating apparatus utilizing microwave power comprising: a plurality of solid state modules of the type which when biased generate microwave signals and heat, a terminal coupled to said modules and adapted to be coupled to a bias source for providing biasing of said modules, an enclosure having walls adapted to receive a body to be heated, one of the inner surfaces of one of said walls being constructed of electrically conductive and heat conductive material and being configured to dissipate heat into said enclosure, said plurality of solid state modules being fixed to said one inner surface of said one wall so that said heat generated from said modules is dissipated by said one inner surface of said one wall and in said enclosure for causing conventional heating of said body, at least one microwave antenna being coupled to said modules and responsive to said generated microwave signals for radiating said microwave signals into said enclosure for causing microwave heating of said body.
 2. The combination as claimed in claim 1, wherein means are provided for adjusting the operating characteristic of the modules for controlling the ratio of microwave heating to conventional heating in the enclosure.
 3. The combination as claimed in claim 1, wherein said antenna is a dipole.
 4. The combination as claimed in claim 3, wherein said inner surface of said one wall is cylindrically shaped to act as a cylindrical reflector for said dipole.
 5. Heating apparatus utilizing microwave power comprising: an enclosure having a multilayered side wall adapted to receive a body to be heated, and a plurality of solid state modules of the type which when properly biased generate microwave signals and heat, means for properly biasing said modules, the innermost surface layer of said side wall being a metal conductor, the next outer layer adjacent said innermost layer being of dielectric material having on its outermost surface a network of narrow strip-like conductors joining said plurality of solid state modules to each other and forming with said dielectric layer and said innermost surface layer a transmission line network for combining the microwave signals generated by each of said plurality of solid state modules, said solid state modules being fixed to said innermost surface of said multilayered side wall so that heat generated from said modules is dissipated in said enclosure for causing conventional heating of said body, at least one microwave antenna being coupled to said modules over said transmission line network and being responsive to said microwave signals for radiating said microwave signals generated at said modules into said enclosure and thereby causing microwave heating of said body.
 6. Heating apparatus utilizing microwave power comprising: an enclosure adapted to receive a body to be heated having a cylindrically shaped side wall, a top wall and a bottom wall, at least four clusters of solid state modules of the type which when properly biased generate both microwave signals and heat, means for properly biasing said modules, the inner surface of the cylindrically shaped side wall being metal with ridges therein to dissipate heat into said enclosure, each of said clusters of solid state modules being equally spaced from each other about said cylindrical wall with said modules being fixed to said inner surface of said cylindrically shaped side wall so that said heat generated from said Modules is dissipated in said enclosure for causing conventional heating of said body, at least four microwave antennas spaced from and distributed equally about the inner surface of said cylindrical side wall and extending into the interior of said enclosure, means for coupling each of said antennas to only one of said clusters of solid state modules so that microwave signals generated by said modules radiate from each of said antennas into said enclosure for causing microwave heating of said body.
 7. Heating apparatus utilizing microwave power comprising: a spherically shaped enclosure adapted to receive a body to be heated, the inner surface of said enclosure being of electrically conductive and heat conductive material and being configured to dissipate heat into said enclosure, a plurality of solid state modules of the type which when properly biased generate microwave signals and heat, said modules being fixed to said inner surface of said spherically shaped walls so that said generated heat from said modules is dissipated uniformly in said enclosure for causing conventional heating of said body, means for properly biasing said modules, antenna means equally spared from each other and uniformly distributed from and about said inner surface of said spherically shaped enclosure, each of said antennas being coupled to a given number of modules and responsive to said microwave signals generated by said modules for radiating said microwave energy into said enclosure for causing microwave heating of said body. 